The present invention relates, in general, to expandable electrode bodies used in ablating body tissue and methods of manufacturing the same, and, in particular, to expandable electrode bodies for ablating pulmonary vein tissue and related tissue and methods of manufacturing the same.
Normal sinus rhythm of the heart begins with the sinoatrial node (or xe2x80x9cSA nodexe2x80x9d) generating a depolarization wave front, or electrical impulse. This impulse causes adjacent myocardial tissue cells in the right and left atria to depolarize. The electrical impulse uniformly propagates across the right and left atria and the atrial septum to the atrioventricular node (or xe2x80x9cAV nodexe2x80x9d), causing the atria to contract and empty blood from the atria into the ventricles. The electrical impulse propagates through the AV node to the atrioventricular bundle (or xe2x80x9cHIS bundlexe2x80x9d), where it further propagates across the ventricles, causing the ventricles to contract. The AV node regulates the propagation delay to the HIS bundle, so that atrial systole occurs during ventricular diastole. This coordination of the electrical activity results in the described, organized sequence of myocardial contraction leading to a normal heartbeat.
Sometimes aberrant conductive pathways develop in heart tissue, which disrupt the normal path of depolarization events. For example, anatomical obstacles, called xe2x80x9cconduction blocks,xe2x80x9d can cause the electrical impulse to degenerate into several circular wavelets that circulate about the obstacles. These wavelets, called xe2x80x9creentry circuits,xe2x80x9d disrupt the normal activation of the atria or ventricles. As a further example, localized regions of ischemic myocardial tissue may propagate depolarization events slower than normal myocardial tissue. The ischemic region, also called a xe2x80x9cslow conduction zone,xe2x80x9d creates the substrate for errant, circular propagation patterns, called xe2x80x9ccircus motion.xe2x80x9d The circus motion also disrupts the normal depolarization patterns, thereby disrupting the normal contraction of the heart tissue.
The aberrant conductive pathways create abnormal, irregular, and sometimes life-threatening heart rhythms, called arrhythmias. An arrhythmia can take place in the atria, for example, as in atrial tachycardia (AT) or atrial flutter (AF). The arrhythmia can also take place in the ventricle, for example, as in ventricular tachycardia (VT). In treating arrhythmias, it is sometimes essential that the location of the sources of the aberrant pathways (called focal arrhythmia substrates) be located. Once located, the focal arrhythmia substrate can be destroyed, or ablated, e.g., by surgical cutting, or the application of heat. In particular, ablation can remove the aberrant conductive pathway, thereby restoring normal myocardial contraction. An example of such an ablation procedure is described in U.S. Pat. No. 5,471,982, issued to Edwards et al.
Alternatively, arrhythmias may be treated by actively interrupting all of the potential pathways for atrial reentry circuits by creating complex lesion patterns on the myocardial tissue. An example of such a procedure is described in U.S. Pat. No. 5,575,810, issued to Swanson et al.
Frequently, a focal arrhythmia substrate resides at the base, or within, one or more pulmonary veins, wherein the atrial tissue extends. The automaticity created by these substrates results in ectopic atrial tachycardia. Although the effect caused by the depolarization wavefront propagating from the pulmonary vein containing the substrate resembles that caused by re-entrant pathways within the atria, the atrial fibrillation is actually caused by a single focal arrhythmia substrate within the pulmonary vein. Arrhythmia substrates residing at the base of, or within, a pulmonary vein may alternatively participate in circuit with the depolarization wavefront propagating around a single vein or within a slow conduction zone residing near or within the vein.
Current techniques of eradicating these substrates include steering a conventional ablation catheter within the target pulmonary vein, mapping this region to pinpoint the substrate, and ablating targeted tissue. However, this is a time consuming and difficult process. Either extensive mapping must be performed within the pulmonary vein to accurately locate the target ablation site, or multiple lesions must be created to, in effect, xe2x80x9ccarpet bombxe2x80x9d the substrate. Moreover, the substrate may be located deep within the pulmonary vein, thereby making the manipulations required to steer the catheter""s distal tip to the target site difficult.
Another technique involves creating circumferential lesions in endocardial and surrounding tissues, e.g., in and around pulmonary veins, in the inferior vena cava, the superior vena cava, and the sinus coronary, to thereby isolate focal arrhythmia substrates. A variety of catheters with electrodes mounted on their distal ends may be used in performing this technique, an especially popular type being balloon catheters. When balloon catheters are used, at least a portion of the surface area of the balloon typically comprises an electrode that performs the ablation.
A drawback of a conventional electrode balloon for creating circumferential lesions in endocardial and surrounding tissues is that different-sized electrode balloons are required for the different-sized veins and arteries. U.S. Pat. No. 6,012,457 to Lesh proposes using an elastic electrode balloon that may be expanded to different-diameter sizes to accommodate different-diameter ablation areas. Lesh separately discloses porous fluid electrodes through which electrically conductive fluid flows out of the balloon. The electrically conductive fluid serves as a conductive medium for transferring RF energy to surrounding body tissue. A problem with porous fluid electrodes if they are used with an elastomeric balloon material is that the pore size in more relaxed areas of the balloon is smaller than the pore size in more expanded areas of the balloon. Therefore, it is very difficult to control the RF energy delivery using such a balloon. Elastomeric materials expand from a weak point or area and stretch to other areas. The pore size in the weak initiation point or area is larger than the pore size in other areas. As a result, flow of conductive fluid through the pores in the initiation area is greater than the flow of conductive fluid in the other areas, causing energy delivery to not be uniform around the circumference of the balloon. The resulting lesion may not be uniform, may not be circumferential, and/or may not be contiguous. Another problem with the ablation elements or electrodes discussed in Lesh is that they do not allow for alternative ablation element configurations to be easily and inexpensively incorporated into a balloon electrode assembly. The metal ablation element discussed in Lesh requires a conductive lead connected to the ablation element on the outer surface of the balloon. This complicates manufacturing of the balloon. Further, if a metal ablation element is used with an elastomeric balloon, the conductive lead may break upon expansion of the balloon.
Accordingly, there is a need for an expandable elastomeric electrode body that can electrically isolate veins by creating circumferential lesions in tissue, such as in endocardial and surrounding tissue, that can be used over a wide range of different-sized veins, and that allows for alternative conductive configurations to be easily and inexpensively incorporated into a balloon electrode assembly.
An aspect of the invention involves a balloon body of an electrode assembly. The balloon body includes an elastomeric non-conductive body expandable to a wide variety of working diameters to accommodate a wide variety of anatomical structures. The elastomeric non-conductive body has a circumferential region and an interior adapted to receive an electrically conductive fluid medium for expanding the elastomeric non-conductive body and transmitting electrical current therethrough. A plurality of holes are located in the circumferential region of the elastomeric non-conductive body and a conductive elastomeric material covers the holes and forms one or more conductive regions adapted to transmit electrical current received from the electrically conductive fluid medium through the plurality of holes to adjacent body tissue.
Another aspect of the invention involves a method of manufacturing a balloon body of an electrode assembly. The method includes dipping a mold in an elastomeric non-conductive solution so as to form an elastomeric non-conductive body, creating a plurality of holes in a circumferential region of the elastomeric non-conductive body, and covering the holes with a conductive elastomeric material so as to form one or more conductive regions on the elastomeric non-conductive body.
Other and further objects, features, aspects, and advantages of the present inventions will become better understood with the following detailed description of the accompanying drawings.